Case Study: Soil Analysis

Soil analysis can provide information about the mixture of solids (minerals and organic matter), liquid and gasses that make up the soil. Soil analysis is helpful because it is important to know the types of minerals that are in the soil and how to treat the soil, including which minerals to add and which minerals to remove from the soil. Many minerals are beneficial and provide nutrients to the soil, but some minerals, such as asbestos, can be hazardous to people.

There are numerous types of asbestos minerals. Asbestos minerals are all silicate minerals, and they range in size and chemical composition. Asbestos minerals are durable, long, thin fibrous crystals and are divided into two categories: serpentine asbestos and amphibole asbestos. Serpentine asbestos is made up of long, curly fibers. Due to its flexibility, it was used in many products. Amphibole asbestos is made of brittle, rod- or needle-shaped fibers.

THE PROBLEM:

A client was concerned about the presence of asbestos in their soil. They wanted to know if there were any fibers present in the soil and wanted to know their aspect ratios (length/width).

THE ANALYSES:

The first step in examination was dividing the sample into sub-samples based on grain size. We used 1 mm and 300 µm sieves to generate three separate sub-samples for analysis (Figure 1): coarse (>1 mm), intermediate (300 µm – 1 mm) and fine (<300 µm).

The coarse fraction (Figure 2) was analyzed by stereomicroscopy, shown in the larger image, and polarized light microscopy (PLM), shown in the smaller image. The intermediate fraction was analyzed by PLM (Figure 3). The fine fraction was analyzed by PLM and transmission electron microscopy (TEM) (Figure 4).

THE OUTCOME:

Possible asbestos fibers were identified using PLM (Figure 3) and confirmed at chrysotile using TEM (Figure 4).  Much of the chrysotile was in the form of bundles with aspect ratios greater than 3:1.

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